Several protocols exist in which one computer (a “host”) receives and processes requests from a number of other computers (“clients”). For example, in applications involving the world-wide web, a server can receive and process many concurrent requests from different users on the internet. In this example, the server would be the host while each user device would be a client.
Requests can usually be grouped into sessions, with each session each having one or more related requests. For example, a multiple-request session could consist of a request requesting information over the world wide web, and an associated response. Alternatively, a multiple-request session could consist of a commercial transaction, with related requests respectively used to locate a web site for a precise product, submit an order or billing and shipping information, and convey a confirmation of sale to a particular client. Whether a host is to process just a single request or a series of related requests, is usually important to quickly; accurately and completely service each request and each session.
The term “quality of service” refers a host's ability to provide quick and consistent responses to a request, complete a session and consistency in doing so. As a particular host becomes more popular, and due to that popularity receives more requests, the host's processing resources can become stretched. For example, due to heavy traffic, a host may not be able to respond to a request at all, or the host may not provide a timely response (which can cause a client to “time-out” and generate an error). Poor quality of service can have significant consequences, as users may become frustrated and simply give up trying to reach a particular host, or the sponsor of the host may lose sales or fail to communicate needed information to any or all clients.
Two techniques are generally used to alleviate quality of service problems. First, more processing capacity can be added to the host, typically by either replacing the host with another, more powerful computer or by providing multiple computers in parallel and delegating new requests to different ones of the multiple computers. While this first technique presents an effective way of reducing some quality of service problems, it is not always practical. For example, sometimes, due to inadequate planning, budgetary constraints or space constraints, additional processing capacity cannot be added. If demand for a host is not properly forecast, there may be a long lead time before additional processing capacity can be purchased and implemented. Additionally, the processing power may be in the placed inefficiently in the information system.
A second technique calls for applying “admission control,” where only a certain number of client requests are processed (“admitted”) and the remainder are refused; of the requests which are in fact admitted, all are ideally handled in an expedient manner without degradation of quality of service as to those admitted requests. An advantage of this technique is that admission control can be implemented in software, thus facilitating quick, inexpensive use with little advance notice. Unfortunately, typical admission control mechanisms operate by admitting requests on a request-by-request basis, and so, these typical admission control requests do not provide an adequate solution for multiple-request sessions. Also, the requests which are not admitted to the host are generally not handled at all, such that a client is not informed that the request has been refused or the client, if informed, is simply asked to “try again later.” Typically, a refused client must try repeatedly to obtain service with no guarantee that future requests will be processed. For these reasons and others, techniques generally used to alleviate quality of service problems are not always successful. U.S. Pat. No. 6,006,269, incorporated herein by reference, discloses an admission control system having an admission control gateway, a deferral manager and a scheduler. When the admission control gateway receives a request that calls for a new client session, the gateway determines whether a processing threshold has been reached; if the threshold has been reached or surpassed, the request is passed to the deferral manager to formulate a response to the particular client. The scheduler is checked to determine a time when the host can expect to have processing resources available, and the deferral manager then formulates a time indication which tells the client when the client can expect to gain admission to the host.
A need exists for an admission control system having an improved ability to alleviate quality of service problems. In particular, a need exists for an admission control system which responds to all requests, whether or not those requests are actually admitted. Ideally, such system would operate by admitting entire sessions, not just individual requests, such that requests relating to a session in-progress are generally admitted. With a system of this type, admission control would at least provide a reliable means of finishing each session with high quality of service. Finally, a need exists for a system that provides some committed level of service to all clients, including those which may have been initially refused admission.